ICD-10-CM coding guidelines, made simple
All 22 chapters of the ICD-10-CM Official Guidelines for Coding and Reporting, FY 2027 — in tables, with diagrams, coding tips, query prompts, audit notes, multiple-choice questions and coded scenarios.
Master ICD-10-CM is a free, chapter-by-chapter reference to the ICD-10-CM Official Guidelines for Coding and Reporting, FY 2027 (effective October 1, 2026 – September 30, 2027). Every one of the 22 chapters has its own page, as do the conventions, the general coding guidelines, Section II, Section III, Section IV and the Present on Admission guidelines. Each chapter page sets the official rules out in tables, adds coding tips, query prompts and audit notes, then closes with multiple-choice questions and coded scenarios with full rationales — so you can learn a chapter and test yourself on it in one sitting.
Find a chapter or a rule#
Type a condition, a code range or a chapter number. The index below filters as you type — try sepsis, I21, pressure ulcer, POA, Z code or 7th character.
28 pages · all content sourced from the CMS FY 2027 guidelines
No page matches that term. Try a broader word — “sepsis” rather than “septicaemia”, or a code range such as “I10”.
How is this site meant to be used?#
Read the two foundation pages first, then work the chapters in any order. Section I.A (conventions) and Section I.B (general guidelines) govern every chapter, and most coding errors found in audits trace back to one of them rather than to a chapter-specific rule.
1. Guidelines in tables
The official wording, reorganised into decision tables you can scan during coding rather than paragraphs you have to re-read.
2. Diagrams
Sequencing and decision logic drawn out — sepsis, neoplasms, hypertension, obstetrics, 7th characters, POA.
3. Tips, queries, audits
What to watch for, when a query is the correct action, and where auditors and payers find errors.
4. MCQs and scenarios
Five questions and two to three coded scenarios per chapter, each with the answer and a rationale tied back to the guideline.
What changed for FY 2027?#
The FY 2027 guidelines keep the structure of prior years: Section I (conventions, general guidelines, chapter-specific guidelines), Section II (principal diagnosis), Section III (additional diagnoses), Section IV (outpatient) and Appendix I (present on admission). The pages on this site quote and restate the FY 2027 text as published, including the guidelines that carry an explicit “reserved for future guideline expansion” note (chapters 3, 8 and 11) and the two guidelines marked as deleted (Section II.E and Section I.C.18.f).
Who wrote this?#
These pages are written by Dr. Santosh Kumar Guptha — CCS, CCS-P, CPC, COC, CIC, CRC, CPMA, CDIP, CPCO and a first-generation AHIMA-Approved ICD-10-CM/PCS and ICD-11 trainer — founder of MEDESUN® Medical Coding Academy. Twenty-two years in coding, auditing and clinical documentation improvement, roughly one million records overseen, and more than thirty thousand coders trained. Read more about the author.
Frequently asked questions#
Are these the complete official guidelines?
No, and they are not meant to be. This site restates and organises the FY 2027 guidelines with tables, diagrams and practice questions added. The complete official text is a 121-page PDF published by CMS and NCHS — download it here and keep it alongside these pages.
Do the guidelines apply to outpatient coding as well?
Section I — conventions, general guidelines and chapter-specific guidelines — applies in every health care setting unless a guideline says otherwise. Section II and Section III apply to inpatient and other non-outpatient settings. Section IV applies to hospital outpatient and provider office encounters. The clearest difference: uncertain diagnoses are coded as established in the inpatient setting and are never coded in the outpatient setting.
Do the conventions outrank the guidelines?
Yes. The guidelines state it twice: the conventions and instructions of the classification take precedence over the guidelines, and in determining the principal diagnosis the conventions in the Tabular List and Alphabetic Index take precedence over the official coding guidelines. A Tabular instruction beats a guideline; a guideline beats habit.
Can I use this site to prepare for CPC, CCS, CIC, COC, CRC or CPMA?
Yes, for the guideline portion of those exams. Every chapter page ends with exam-style multiple-choice questions and coded scenarios with rationales. What this site cannot replace is a current code book: you still need the Tabular List and Alphabetic Index in front of you, because code selection is verified there, not in a guideline.
Is this site affiliated with CMS, AHIMA or AAPC?
No. Master ICD-10-CM and MEDESUN® Medical Coding Academy are independent and are not affiliated with, endorsed by or certified by CMS, NCHS, CDC, AHA, AHIMA, AAPC, the WHO or any government agency. See the notice in the footer of every page.
Primary sources#
- ICD-10-CM Official Guidelines for Coding and Reporting, FY 2027CMS — the source document for every page on this site (effective 1 Oct 2026)
- NCHS ICD-10-CM files — Tabular List, Index, POA exempt listOfficial code files, addenda and the list of codes exempt from POA reporting
- ICD-10 Coordination and Maintenance CommitteeWhere code proposals are debated; agendas, summaries and meeting materials
- CMS ICD-10 homeCode sets, transition guidance and Medicare coding policy
- AHA Coding ClinicOfficial coding advice from the AHA Central Office — subscription required
- HHS OIG Work PlanActive audit topics — useful for prioritising internal coding audits
- MEDESUN Medical Coding AcademyTraining, credential preparation and audit services by the author